1. Technical Field
The present invention relates to a water-based ink containing a pigment as a coloring material and used for an ink jet printer wherein recording is conducted with a liquid ink.
2. Background Art
In the prior art, an ink comprising water, an organic solvent, a wax or other substance and, dissolved therein, a dye as a coloring agent has been mainly used as an ink for ink jet recording. Such an ink has poor light fastness and water resistance derived from properties of the dye. In order to solve this problem, a proposal has been made on an ink wherein a pigment, such as carbon black or aniline black, was used as the coloring agent. For example, an ink containing a water-soluble polymer in addition to the pigment is described in Japanese Patent Publication No. 15542/1989 and Japanese Patent Laid-Open Nos. 63766/1983, 255875/1990 and 276874/1990.
An ink of a water dispersion system can improve printing density, light fastness and water resistance, etc. as compared with an ink of a dye system. The ink for ink jet recording, however, should have properties such that it does not clog a fine ejection nozzle, has excellent rubbing resistance and setting to dry in the print, is free from aggregation or settlement of solid matter, such as a pigment particle, and exhibits no change in the properties of the ink even when stored at a high temperature or a low temperature for a long period of time and can be redispersed by stirring or further addition of a solvent even when the pigment once aggregated.
The above conventional inks have not yet satisfied all the property requirements of an ink jet printer.